Gas treatment apparatus such as chemical vapor deposition systems are used to treat substrates such as semiconductor wafers. One form of apparatus commonly used is a rotating disk reactor. Such a reactor includes a chamber and a disk-like substrate carrier mounted within the chambers. Substrates such as wafers are disposed on the carrier, and the carrier is rotated about its axis. A component referred to as a gas distribution injector or “injector head” is mounted in fixed position on the chamber. The gas injector head typically includes numerous gas inlets. One or more reactive gases are injected into the chamber through these inlets and flow generally in a downstream direction toward the substrate carrier, and outwardly across the rotating substrate carrier and the surfaces of the substrates disposed on the carrier. Carrier gases may be injected along with the reactive gases.
As the gases pass across the surfaces of the wafers, they react and deposit materials on the wafer surfaces. Merely by way of example, such processes can be used to form compound semiconductors, for example, various layers of compound semiconductors. For example, numerous layers of III-V semiconductors such as gallium nitride, indium nitride, gallium arsenide, indium phosphide and gallium antimonide and the like can be deposited onto a substrate to form electronic devices such as diodes and transistors and optoelectronic devices such as light-emitting diodes and semiconductor lasers. II-VI semiconductors can be deposited by similar processes.
Small differences in the properties of each layer can profoundly affect the performance of the resulting device. The properties which can affect performance include thickness, composition, doping and impurity concentration, crystalline quality and atomic interface abruptness. Therefore, considerable effort has been devoted in the art towards development of apparatus and methods which promote uniform deposition across the entire surface of the wafer carrier. Rotation of the wafer carrier helps assure that the deposition will be uniform in the circumferential direction, around the axis of rotation of the carrier. To assure uniformity in the radial direction along the carrier surface perpendicular to the axis, the gas inlets carrying each of the reactive gases typically are subdivided into a plurality of zones. For example, the gas inlets for a particular gas may be subdivided into several zones in the form of rings concentric with the axis of rotation. The gas flow to each zone may be controlled independently of the other zones. It is possible to select a set of gas flows for the various zones which will provide very nearly uniform distribution across the entire extent of the substrate carrier and thus the entire extent of each substrate or wafer processed.
However, still further improvement would be desirable.